It is well known that, in mining operations, minerals in the form of ores are excavated and processed. These operations generate mineral wastes in a powder or course granular form. These wastes, otherwise referred to as tailings, accumulate as large hills near the mine or mineral processing site. Because the tailings are difficult and expensive to handle and transport over either short or long distances, they are generally left above ground permanently.
The large hills of tailings take up valuable surface area, are unsightly, are subject to rapid erosion and are a potential source of wind blown dust and contamination to the soil, ground water or the surface water. Hence, a method of managing the tailings is desired. Because of their mineral nature, the tailings are relatively dense with a specific gravity normally in the range of 2 to 4. Also, the tailings generally have a particle size ranging from a fine powder to coarse gravel.
In the past, mine tailings have been used as backfill for underground cavities or open pits. In backfill operations, only the coarse fraction of the solid waste material, such as tailings, is transported by gravity, pneumatically conveyed or mechanically pumped into the cavity or pit that is desired to be filled. Because dewatering of the placed fill can be a problem, the fine fraction which is comprised of particles which are smaller that 100 mesh is not generally used as backfill. The fill is typically placed and dammed for containment, and, therefore, requires the construction of underground walls, drainage wells, and the like.
Methods are also known for suspending solid particles in a fluid. For example, in the drilling industry, drilling mud is used to carry particles generated by the drilling process up and out of the well. In that application, the drilling fluid or mud is pumped rapidly to suspend the particles in a continuous cycle down the drill pipe and up the outside of the drill string. Upon reaching the surface, the mud is discharged across a screening plant to a holding pond. The smaller solid particles generated at the bit and not caught by the screens settle from the mud and the mud itself is reclaimed and recycled into the well. Because the solid particles drop out quickly at low velocities and the base fluid or mud is recycled, the amount of mud required to transport the particles from the bottom of the well is not critical. Generally, the weight of particles incorporated into the fluid is in the range of about ten to about fifteen percent of the total weight of the fluid. The velocity of drilling mud under normal operating conditions is in the range of from two to four feet per second.
In the transportation and emplacement of mining tailings, however, there may be no surface recovery and recycling of the base fluid. Furthermore, it is not economical or technically feasible to use large amounts of drilling type muds and high velocity to suspend and dispose of large quantities of solids because the cost is high and the emplacement sites are remote. For example, a drilling mud having a specific gravity of 2.7 and made up of lead solids in water with sufficient clay and polymer additives to suspend those solids can cost about $70.00 to about $80.00 per barrel. Such suspension would require smaller than 100 mesh lead, 25 pounds of bentonite per barrel, approximately 3-4 pounds of a suitable polymer per barrel and 2-4 feet per second velocity to maintain it in suspension. Such a mixture is far too expensive for permanent placement underground and the required velocities cannot be maintained in areas distant from the point of release of the mixture.
According to the present invention, a large quantity of solid particles is suspended in a liquid by using a relatively small amount of clay. The solids can be transported and deposited at a point in a cavity or an open pit and allowed to flow over a large area at low velocity, economically and efficiently.
This and other objectives of the present invention will become apparent from the following description.